The present invention relates to optical communication systems and more particularly to systems and methods for communicating management information via optical links.
The explosion of communication services, ranging from video teleconferencing to electronic commerce is providing rapid growth of Internet traffic. To cope with the rising volume of Internet traffic, service providers are more and more relying on optical technology both in the core network and as a way of accessing network users. To obtain a multiplicative increase in capacity, wavelength division multiplexing (WDM) techniques are being employed where multiple optical signals having disparate wavelengths share the same fiber.
Proper operation of an optical network requires that in addition to payload data, optical links should preferably also carry utility data, e.g., system management information. The utility data may include signal strength information, environmental parameters such as temperature, etc. One prior art approach to carrying utility data across an optical link is to allocate a wavelength to an optical signal modulated with only utility data. This represents a tremendous waste of the optical components needed to receive, transmit, and otherwise process the optical signal because a single wavelength may well be capable of carrying, e.g., 2.5, 10, or more Gbps of payload data for which the service provider could earn revenue whereas the data rate of the utility data may be quite low.
An alternative approach is to modulate an optical signal on a single wavelength with both the payload data and the utility data by use of frequency domain multiplexing. This is presently done using amplitude modulation for both data streams. The transmission of utility data takes advantage of the unoccupied sections of the spectrum of the payload data modulated optical signal. For example, in one approach, both a 5.7 Kbps utility data stream and a 10 Gbps payload data stream amplitude modulates the optical carrier signal. The spectrums of the utility data and of the payload data do not overlap and they may be separated at the receiver using filters.
This latter approach also carries serious drawbacks. For example, it would be desirable to transmit optical equipment firmware updates via the utility data channel. However, the spectrum left unoccupied by the payload data modulation is insufficient to accommodate the data rate necessary for timely transmission of firmware upgrades. Furthermore, the low frequency of the utility data modulation may be within the loop bandwidth of optical amplifier regulation along the link causing optical amplifier gain to undesirably vary in response to the utility data stream. Also, if the flow of payload data ceases for some reason, the optical signal may be subject to superimposed pink (1/f) noise that would swamp the baseband utility data.
What is needed are systems and methods for combining utility data and payload data on an optical communication link such that link capacity is used efficiently, the utility data transmission rate is sufficient to support software upgrades, and problems inherent with relying on baseband transmission of utility data are overcome.